This present invention is directed to an improved method of starting single-phase induction motors.
Many single-phase induction motors have a quadrature winding which is excited by a temporarily-inserted starting capacitor. The starting current of these motors is several times larger than the full-load line current. This high starting current is undesirable for large motors.
The use of starting capacitors for single-phase motors is taught in the U.S. Pat. No. 4,792,740 titled "THREE-PHASE INDUCTION MOTOR WITH SINGLE-PHASE POWER SUPPLY", issued Dec. 20, 1988 to Otto J. M. Smith. The use of starting capacitors for single-phase motors is also taught in U.S. Pat. No. 5,300,870 titled "THREE PHASE MOTOR CONTROL", issued Apr. 5, 1994 to Otto J. M. Smith. The use of starting capacitors for single-phase motors is also taught in U.S. Pat. No. 5,545,965, titled "THREE-PHASE MOTOR OPERATED FROM A SINGLE-PHASE POWER SUPPLY AND PHASE CONVERTER", issued Aug. 13, 1996 to Otto J. M. Smith. In some cases, the high starting current is not objectionable. For all large motors, however, and in many other cases, the high starting current is undesirable. This present invention is directed to an improved capacitor system to reduce the starting current and to improve the starting torque.
This method can be applied to all of the motors in the three U.S. Patents referenced above.